How often does track need to be replaced?

[jis]

Of course all the real high speed tracks in the world carry only 17 - 20 tonne axle load, not 30+ tonne.

True, but it is quite possible to design and build a track that can do both. In fact, it would be easier in quite a few ways to maintain track with this range of axle loads in a non-ballasted track form than a ballasted track. Remember, just because something has not been done, does not mean that it cannot be done.

That is certainly true! Actually there is ballastless track in the US that handles 30+ ton axle load. That would be the LIRR Babylon Branch tracks.